Herein we describe a direct method, promoted by potassium tert-butoxide (KOtBu), for the synthesis of highly substituted α-methylene β-lactams and α-arylidene β-lactams from the amino ester intermediates derived from the acetates and bromo derivatives of the Baylis–Hillman adducts. A variety of β-lactams was synthesized in a single step with good yields.